如何初始化无法访问的模板类的静态成员？

Question

I have code similar to the following, where a class template has a static variable that needs to be initialized. I then have a template class typedef that uses a private, inner class as the template argument:

template <typename T>
class Foo
{
private:
  static const char* s_name;
};

class Bar
{
private:
  class Baz
  {
  // ...
  };

  typedef Foo<Baz> FooBaz;
};

I thought I could initialize the static variable like this:

template<>
const char* Foo<Bar::Baz>::s_name = "foobaz";

And it works... in MS Visual Studio 2015. However, when I build with clang, I get the an error like the following:

Error 'Baz' is a protected member of 'Bar'

Why does this work with MSVS, but not clang? Is there a way to initialize this variable that will work with both?

Answer 1

在“Bar”中公开“typedef Foo FooBaz”并使用“Bar :: FooBaz :: s_name”。

Answer 2

You can always use that, if you do not care about partial instantiation.

template<typename T>
   const char *  Foo<T>::s_name = "foo";

for partials you need to make Foo a friend to Bar.

class Bar
{
private:
    class Baz {
       // ...
    };
    friend class Foo<Baz>;

    typedef Foo<Baz> FooBaz;

};
template<>
    const char * Foo<Bar::Baz>::s_name = "barbaz";